In situ extraction of lithium from the aqueous phase using chemically modified Hylocereus undatus peel: kinetics, thermodynamics and in-field optimization

Lithium is one of the most widely used industrial reagents for energy storage, battery production and electronic materials production. Among various agro-wastes, dragon fruit peel is one of the most promising substitutes for metal recovery. The present study aims to synthesize a novel low-cost and sustainable biosorbent, dragon fruit (Hylocereus undatus) peel impregnated with dibenzoyl methane (DBM), for lithium recovery from the aqueous phase. The biosorbent is characterized using SEM, FTIR, XRD, BET, XPS and DFT calculation techniques to understand the composition, structure and surface complexation. The kinetics study suggested that adsorption followed pseudo-second order kinetics with a correlation coefficient (R2) value of 0.99 and a rate constant of 29.28 x 10-4 g mg-1 min-1. The isotherm studies evaluated the reaction to be heterogeneous with effective binding energies as depicted by Freundlich and Temkin isotherm models. The mechanistic forces include weak van der Waals forces, metal-surface complexation and valence forces. The thermodynamics study revealed the process to be exothermic (Delta H degrees = -18.28 kJ mol-1) and spontaneous with negative Gibbs free energy values. The maximum lithium uptake capacity was found to be 13.6 mg g-1. Acidic media favoured the recovery of the metal ion up to three cycles. The long term stability study using a fixed bed column showed 84% lithium extraction efficiency for the CMB. The lab scale study is validated using the CMB for lithium extraction from the real geothermal water sample of the Dholera region, Gujarat.